Re: [PATCH v2 1/1] x86/fred: Fix system hang during S4 resume with FRED enabled

[Rafael J. Wysocki]

On Tue, Apr 1, 2025 at 9:57 AM Xin Li (Intel) <xin@xxxxxxxxx> wrote:
>
> Upon a wakeup from S4, the restore kernel starts and initializes the
> FRED MSRs as needed from its perspective.  It then loads a hibernation
> image, including the image kernel, and attempts to load image pages
> directly into their original page frames used before hibernation unless
> those frames are currently in use.  Once all pages are moved to their
> original locations, it jumps to a "trampoline" page in the image kernel.
>
> At this point, the image kernel takes control, but the FRED MSRs still
> contain values set by the restore kernel, which may differ from those
> set by the image kernel before hibernation.  Therefore, the image kernel
> must ensure the FRED MSRs have the same values as before hibernation.
> Since these values depend only on the location of the kernel text and
> data, they can be recomputed from scratch.
>
> Reported-by: Xi Pardee <xi.pardee@xxxxxxxxx>
> Reported-by: Todd Brandt <todd.e.brandt@xxxxxxxxx>
> Suggested-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
> Signed-off-by: Xin Li (Intel) <xin@xxxxxxxxx>
> Tested-by: Todd Brandt <todd.e.brandt@xxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Brian Gerst <brgerst@xxxxxxxxx>
> Cc: Juergen Gross <jgross@xxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # 6.9+

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

> ---
>
> Change in v2:
> * Rewrite the change log and in-code comments based on Rafael's feedback.

Thanks!

> ---
>  arch/x86/power/cpu.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
> index 63230ff8cf4f..08e76a5ca155 100644
> --- a/arch/x86/power/cpu.c
> +++ b/arch/x86/power/cpu.c
> @@ -27,6 +27,7 @@
>  #include <asm/mmu_context.h>
>  #include <asm/cpu_device_id.h>
>  #include <asm/microcode.h>
> +#include <asm/fred.h>
>
>  #ifdef CONFIG_X86_32
>  __visible unsigned long saved_context_ebx;
> @@ -231,6 +232,19 @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
>          */
>  #ifdef CONFIG_X86_64
>         wrmsrl(MSR_GS_BASE, ctxt->kernelmode_gs_base);
> +
> +       /*
> +        * Reinitialize FRED to ensure the FRED MSRs contain the same values
> +        * as before hibernation.
> +        *
> +        * Note, the setup of FRED RSPs requires access to percpu data
> +        * structures.  Therefore, FRED reinitialization can only occur after
> +        * the percpu access pointer (i.e., MSR_GS_BASE) is restored.
> +        */
> +       if (ctxt->cr4 & X86_CR4_FRED) {
> +               cpu_init_fred_exceptions();
> +               cpu_init_fred_rsps();
> +       }
>  #else
>         loadsegment(fs, __KERNEL_PERCPU);
>  #endif
>
> base-commit: 535bd326c5657fe570f41b1f76941e449d9e2062
> --
> 2.49.0
>